If body contains certain string check if it contains other string

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My question:
I’m trying to write a test based on the output of a html body.
In that body there are 2 keys with their values I like to assert, weatherType and weatherIcon.
If weatherIcon has value B, C, D or E, the weatherType should be “Bewolkt”.
If weatherIcon has other values, the weatherType is different.

How can I easily do this in Postman?
I can work with a lot of If statements, but there should be a better option no?
I can’t turn the body into JSON because its just one object “html”.

Details (like screenshots):

"temperature":15,"weatherIcon":"C","weatherType":"bewolkt"}

How I found the problem:

I’ve already tried: